1. Field of the Invention
The present invention relates to an electric power steering device that includes a steered shaft that is provided in a metallic housing so as to be capable of reciprocating motion, an electric motor that is attached to the housing, a ball screw device that converts rotation of the electric motor into rectilinear motion of the steered shaft, and a rolling bearing that rotatably supports the ball screw device on the housing.
2. Description of Related Art
Japanese Patent Application Publication No. 2005-343308 (JP-A-2005-343308), for example, discloses an example of the ball screw device described above.
There also has been proposed an electric power steering device in which a steering assist force that is generated by driving an electric motor is added via a belt to a steering force that is generated by operating a steering wheel to perform steering (see Japanese Patent Application Publication No. 2005-343434 (JP-A-2005-343434), for example). In the electric power steering device according to JP-A-2005-343434, the belt is wound around a driving pulley that is provided on a rotary shaft of the electric motor and a driven pulley that is provided on a ball screw nut that is fitted with a threaded portion of a rack shaft via balls. A driving force of the electric motor rotates the ball screw nut via the belt, along with which the rack shaft which includes the threaded portion is driven in the axial direction to assist steering.